Like other perishable agricultural commodities, sugar beets deteriorate in storage. The general estimate is that beets lose about one half pound of sugar per ton per day of storage, or fifty pounds of sugar per ton of beets during a 100 day storage period.
When sugar is 12.cent. per pound, this loss amounts to $6.00 per ton for the 100 day storage period. If average yield is 20 tons per acre and growers receive 60% of the value of the sugar, then the loss amounts to $72 per acre to the grower, $48 per acre to the processor.
Although storage losses can never be totally eliminated, they can be reduced by careful harvesting and handling. This is true even when beets are to be processed immediately after harvesting. Sugar losses are high initially, decrease gradually as the beets are held in storage, and then gradually increase towards the end of the storage period.
A series of studies were conducted by the University of Idaho and cooperators in 1975 and 1976 to determine the extent of injuries to sugar beets during harvesting and handling, and the affect these injuries have on sugar losses. Mechanical damage was evaluated by several methods--by measuring sucrose and impurities in storage, by measuring respiration, and by visual assessment. These studies have helped to point out the problem areas where mechanical injury is most severe.
The University work clearly demonstrates that handling systems now in use severely damage beets, resulting in high sugar losses during storage. In a 1975-76 storage study, beets that were untopped, hand-harvested, damage free, and treated with a fungicide lost less than 0.13 pound sugar/ton/day during 140 days in an environmental storage chamber. Beets that had been mechanically harvested, piled with conventional equipment, and treated with a fungicide lost 0.4 pound/sugar/ton/day; mechanically harvested piled beets without the fungicide treatment lost 1.1 pound/sugar/ton/day.
Damage levels increase at each step of the handling system. By the time beets are in the storage pile, each beet will have several damaged areas.
Preliminary studies suggest that some harvesters damage beets more than others. The difference is most likely caused by the cleaning systems. Machines that use steel rinks and star wheels damage beets more severely than harvesters that use grab rolls. In general, the more cleaning rollers and rinks, the more damage to the beets. Lifter loader harvesters show increased damage to roots taken off the cleaning screens and another increase as roots go into the truck. Tank type harvesters increase damage as the roots are cleaned and elevated to the tank. Damage is also different between the top and bottom of the tank. The lifter loader machine is inherently a lower damage machine than the tank type because the roots are handled less.
For normal conditions, all harvesters do a good job of removing dirt. However, tare studies indicate that harvester cleaning actually isn't needed except to reduce the amount of dirt carried to and from the piling ground.
About one third of the damage during harvesting occurs on the cleaning screen and lifting wheels, another third while moving the beets from the harvester to the truck, and the final third while moving them from the truck to the pile.
The three chief causes of damage to roots while harvesting and handling are: (1) dropping or throwing the roots; (2) striking or scraping the roots with the moving part of the machine; (3) handling the beets when they are cold.
Since the beet harvest occurs late in the fall and the harvest time is limited by weather, stopping harvest because of low temperatures generally is not feasible. However, mechanical systems can be improved to reduce damage.
Changes in equipment occur very slowly. Manufacturers are reluctant to make investments in new systems because the total sales of sugar beet handling equipment is very low. A new improvement in existing sugar beet harvesting machinery that would reduce injury to the beets while maintaining harvester cleaning ability and volume is much needed by the sugar beet industry.